"In hindsight, if anything might have helped stop 9/11, it would have been better information about threats inside the United States -- something made difficult by structural and legal impediments that prevented the collection and sharing of information by our law enforcement and intelligence agencies."

Concerns that terrorists may use airplanes as weapons may have existed in the intelligence community before September 11, 2001, but "to the best of my knowledge this kind of analysis ... actually was never briefed to us."

In the days after the attacks, the Bush administration considered the involvement of Iraq, but never "pushed anybody to twist the facts."

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Rice says President Bush 'never pushed anybody to twist the facts' on Iraq.

WASHINGTON (CNN) -- Under sometimes sharp questioning, national security adviser Condoleezza Rice testified Thursday that there was "no silver bullet" that could have stopped the attacks of September 11, 2001.

"Had we thought that there was an attack coming in Washington or New York, we would have moved heaven and earth to try and stop it," Rice told the independent commission investigating the attacks.

But Rice was pressed repeatedly about an intelligence memo presented to President Bush one month before the attacks, a document that referred to al Qaeda, Osama bin Laden and possible hijackings.

The existence of that August 6, 2001, memo, called a presidential daily briefing, has been reported before, but details about it came out Thursday.

Asked by Democratic commissioner Richard Ben-Veniste, a former Watergate prosecutor who has read the memo, to recall the title, Rice said: "I believe the title was 'Bin Laden Determined to Attack Inside the United States.' "

Family members of some 9/11 victims could be seen shaking their heads in the hearing room as they heard those words.

More than 3,000 people were killed on September 11, 2001, when 19 terrorists hijacked four commercial U.S. jets and crashed them into New York's World Trade Center, the Pentagon and a field in western Pennsylvania.

Rice insisted the memo did not give any advance warning of what was to happen.

"It did not warn of attacks inside the United States," Rice said. "It was historical information based on old reporting."

Later, however, Democractic commissioner Bob Kerrey, a former senator from Nebraska, said the memo told the president "that the FBI indicates patterns of suspicious activity in the United States consistent with preparations for hijacking."

The panel asked the White House to declassify the document. Thursday afternoon, a spokesman for the National Security Council said the administration was "actively looking at the declassification process" and hoped to release it.(Full story)

Clinton testimony

The commission also heard Thursday from former President Clinton, but that three-hour session was in private.

"The commission found the former president forthcoming and responsive to its questions," said a statement issued by the commission. "We appreciate the excellent cooperation he and his associates have given to us."

In the public session, Rice was unyielding in her defense of the Bush administration, insisting it had done all it could to thwart terrorism.

And she offered no apology to 9/11 family members, something her one-time subordinate, former White House counterterrorism adviser Richard Clarke, did in his appearance two weeks ago.

Instead, Rice spoke of the "sorrow and the anger" that she felt the day of the attacks, and at the conclusion of her testimony she offered her condolences to some 9/11 family members.

She repeatedly referenced the 233 days the administration was in office when the attacks occurred. She said there was no way Bush could have instituted the kind of systemic and bureaucratic changes needed in government to address terrorism during that time.

"There was no silver bullet that could have prevented the 9/11 attacks," Rice testified.

She said that the USA Patriot Act , the creation of the Department of Homeland Security -- which Bush initially opposed -- and other reforms in the FBI and CIA have helped solve those problems, but that there is more to do.

Rice said that CIA Director George Tenet briefed Bush almost daily and that the president's "very first major national security policy directive" called for the elimination of al Qaeda. (Transcript of Rice's opening comments)

In a somewhat heated exchange, Ben-Veniste asked Rice if she had told the president about warnings from Clarke that al Qaeda cells were operating in the United States.

Ben-Veniste stopped her to repeat the question when she began to respond with a broader answer.

She testified that she did not remember whether she discussed with Bush concerns about al Qaeda cells inside the United States.

"I don't remember the al Qaeda cells being something that we were told we needed to do something about," she said.

Rice said that the FBI was pursuing the cells and that 70 full field investigations were under way.

Rice also sparred with Kerrey, who took issue with Rice's repeatedly quoting Bush that he was "tired of swatting at flies" and that he demanded a more comprehensive strategy to attack the terrorist network.

Kerrey pointed out there was no U.S. response to the October 2000 bombing of the destroyer USS Cole, which killed 17 American sailors, an attack blamed on al Qaeda.

"What fly had he swatted?" asked Kerrey, a former Democratic senator from Nebraska. "We only swatted a fly once, on the 20th of August 1998. We didn't swat any flies afterwards. How the hell could he be tired?"

Rice responded that the president meant that the United States should do more than just respond to individual terrorists.

Kerrey was referring to the cruise missile attacks of August 20, 1998, ordered by President Clinton on suspected al Qaeda sites in Afghanistan and Sudan in retaliation for the bombings of the U.S. embassies in Kenya and Tanzania two weeks before.

Following Clarke

Clarke testified two weeks ago that the administration failed to heed his warnings about terrorist threats before 9/11.

Clarke, in his testimony and in his newly released bestseller, "Against All Enemies," also charged that Bush undermined the war on terrorism by invading Iraq instead of focusing on al Qaeda, the terrorist network led by Osama bin Laden. (Clarke's testimony)

Committee Chairman Thomas Kean, a Republican, asked Rice if the United States focused too much attention to Iraq following the attacks.

Rice said that it was reasonable to question whether Iraq was involved "given our hostile relationship."

She said that no one "pushed anybody to twist the facts."

Rice told the commission that a plan to attack al Qaeda that Clarke presented to her soon after the Bush administration took office had some elements the new administration adopted, but others that would have led the country "off course."

Instead, she said, the Bush administration focused on a regional approach to al Qaeda.

She said Bush tried to cultivate ties with Pakistani President Pervez Musharraf early in his administration, hoping Musharraf would pressure Afghanistan's ruling Taliban into denying al Qaeda the safe haven it allowed.

White House turnaround

The White House initially resisted calls for Rice's public testimony, arguing it would be a violation of executive privilege.

But the commission, Democrats, some family members of 9/11 victims and even some Republicans called on the administration to reverse its position.

The testimony came roughly seven months before a presidential election in which national security has emerged as a hotly contested issue.

In his bid for re-election, Bush is casting himself as an uncompromising leader on national security, while Democrats charge his efforts have been misguided with mixed results.

Congress created the commission -- initially opposed by the Bush administration -- in November 2002 and charged it with coming up with an authoritative account of the 9/11 attacks, including any security and intelligence lapses.

The panel, formally titled the National Commission on Terrorist Attacks Upon the United States, is also required to issue recommendations on how to protect against any future attacks.

The commission's report is due by July 26, but it may not be released at that time, subject first to a security review by the White House.